For example, parking assistants, which detect objects located in a space laterally adjacent to the driving path of a vehicle, in order to find a parking space (PSL, “parking space localization”) fall in the field of driver assistance systems. These or other assistants additionally carry out object detection in order to make guiding or operability of the vehicle easier, to avoid accidents, etc. For this purpose, objects such as other (parked) vehicles, stationary structures, for example, curbsides, walls, hedges, buildings, vegetation, but also humans are to be detected, who are currently moving through a potential parking space. After successful detection, the driver is informed about the detected objects, for example, by an acoustic or visual display. Active assistance (sub)systems also engage to assist in the vehicle guiding based on the detection, for example, by acceleration, braking, or steering.
In the case of an ultrasound-based system, a plurality of ultrasound sensors is typically attached in a front and/or rear area. In particular, at least one sensor is located in most cases laterally or diagonally to the driving direction, for example, on a front fender of the vehicle. This sensor measures the space adjacent to the driving lane, in that measuring signals are emitted at certain time intervals as the vehicle passes, for example, in the form of pulsed energy emissions. The distance between object and sensor and therefore to the vehicle may be determined from the propagation time of the signal reflected from an object in the surroundings of the vehicle.
In order to be able to determine a direction toward the object in addition to an object distance, the sensor should have a particularly high sensitivity in precisely one (narrow) solid angle range, i.e., the sensor should have a pronounced directional characteristic. However, more frequent measuring pulses must accordingly be emitted in the case of a pronounced directional characteristic, in order to be able to reliably detect objects located laterally adjacent to the driving lane. The maximum pulse frequency is in turn delimited in particular if ultrasound is used due to its comparatively low propagation speed in comparison to electromagnetic radiation such as radar or infrared. Therefore, reliable detection is no longer ensured at a relatively high speed in the case of high location resolution because of the narrow directional characteristic.
A less pronounced directional characteristic having a larger aperture angle and/or multiple angle ranges, which are distributed over the solid angle, having comparatively high sensitivity (i.e., multiple “lobes” or “fingers”) is typically accompanied by generally decreased sensitivity, i.e., range. In the case of a diffuse or multi-finger directional characteristic, it is also no longer possible to determine the direction toward the object with the desired high precision. To increase the precision, complex configurations are necessary, for example, parallel measurements using multiple sensors must be provided, other radiations such as radar or infrared being used in addition to ultrasound, if necessary. This results in high costs for such assistance systems.